Recent optical and structural investigations have shown that ; oth high- and low-temperature forms of plagioclase can exist naturally over the range An0-70, and in the more basic plagioclases (An70_90) Gay (1954) has shown that a structural distinction can be effected although no definite optical differences have yet been established. In the anorthite range slight optical and distinct structural differences have been observed between synthetic plagioelases and crystal lapilli on the one hand and all other natural plagioclases on the other (Gay, 1953).

Bultfonteinite from Bultfontein mine, Kimberley, South Africa, is a hydrated fluorine-containing calcium silicate, of approximate composition Ca4Si2O10H6F2. It was first described in 1932 by Parry, Williams, and Wright,1 who gave an account of its morphology, optical properties, composition, and chemical relationships. It is triclinic but markedly pseudo-orthorhombic. The present work consists primarily of a determination of the unit-cell dimensions, involving a more accurate evaluation of the interaxial angles than the earlier one; this is followed by some tentative suggestions about the structure.

Wadeite has been found only in a suite of leucite-lamproites from the West Kimberley area of Western Australia. The leucite-bearing rocks occur at a number of isolated volcanic vents that have in every instance broken through sedimentary deposits of Permian age. The nature of the mineral, wadeite, has been described by Prider. It is a potassium-zirconium silicate occurring as highly birefringent prisms up to 1 mm. in length with hexagonal-shaped basal sections. It is invariably replaced in part along the poor pyramidal cleavages by calcite.

Thirty-Four specimens of australites were collected by Miss N. Jones and her brother Mr. Jones, during forty years while working on their property of 2000 acres, on the north bank of the Glenelg river. This is situated 3½ miles due east of Harrow (37° 8' S., 141° 33' E.) in the western district of Victoria, 236 miles north of west of Melbourne. The collection was kindly submitted for examination through Mr. E. D. Gill of the National Museum, Melbourne.

Studies of the effect of dehydration at temperatures greater than 150° on sorption by montmorillonites have shown that small interlayer cations such as lithium and magnesium promote an irreversible decrease in the amount of interlamellar sorption and a consequent marked fall in the cation exchange capacity as measured by conventional methods (1, 2, 3, 4). The other minerals of the group do not show this property (4), which is quite distinct from the supposed 'potassium fixation' reported in these minerals (5). This latter effect, which is small for montmorillonite, refers to the decreased rate of exchange of potassium as compared with smaller exchange cations especially after the potassium-saturated mineral has been dried at ]00° C., and has been shown to be much more marked in mica-like minerals with silicate layers of higher charge density (e.g. illites and vermiculites (6)). The amount of water sorbed by potassium-saturated montmorillonite is not significantly affected by drying at temperatures below 400° C. although it is less than that of most other montmorilIonites (3), due probably to the low hydration energy of the potassium ion (7).